Fix bindir check logic, and relax non-bindir case for AIX.

Fix bindir check logic, and relax non-bindir case for AIX.

* tests/bindir.at (bindir install tests): Rewrite checks for
place of the installed shared library in two separate tests,
depending on whether -bindir is supposed to have an effect or
not.  In the positive case, make the test stricter so that we
reject libraries in $libdir.  In the negative case, do not
require a major version number in the $libdir file name, for AIX
without runtimelinking.  If tmpdir creation fails, skip the
test.  Use fewer bindir directory names for testing, to speed
up the test.  Also mention MSVC style DLL name in comment.
Report by Peter Rosin.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>